How my Sim acted autonomsly and according to his personality... How only my slob sims could take a quick shower in the sink, how he would never make the bed or the dishes
How it was harder to form a relationship if they had opposite traits or how you could find out what other traits an NPC had. Was actually difficult and the reward to find it out quicker made sense.
How a heavy sleeper would never wake from noises and light sleeper always. Or how you could go to therapy and breath in a bag if you gave your sim the unstable trait. How you could check the stove for safety if your sim was erratic? Or how your Sim would stop his tasks that you gave him because he was absent minded.
Things like that were cute.